A position detecting device obtains information from a stylus when the stylus moves at high speed, while removing influences of noise. The position detecting device includes a differential amplification circuit that amplifies and outputs a difference in a signal at a first terminal and a signal at a second terminal, and a selection circuit that selects at least a first electrode of a sensor, connects at least the first electrode to the first terminal of the differential amplification circuit, selects at least a second electrode of the sensor, and connects at least the second electrode to the second terminal of the differential amplification circuit. The selection circuit selects electrodes separated by a first interval in a period in which a position indicated by the stylus is detected, and selects electrodes separated by a second interval that is shorter than the first interval in a period in which data is detected.